Internal combustion engines have an air intake system that directs ambient air to the combustion cylinders. Since the tubular shapes of air induction systems may be complex, the flow of air through the system may develop chaotic features that affect how the fluid interacts with the surface of the tube through which it flows. For instance, airflow through a composite intake manifold may develop pressure fluctuations within the cavity and introduce turbulent features into the airflow pattern in a manner that depends on the shape of the cavity. The turbulence induced may then affect how the air transfers its energy to the surface and in response, vibrations may develop in the walls that produce sound radiations in certain regions of the frequency spectrum. The vibrational modes and sound frequencies may further depend on the geometric arrangement of the tube and the velocity of air flow past the surface. Sound radiated from the surface may be considered undesirable noise.
Some approaches aimed at reducing turbulent noise in the engine manifold system involve increasing the structural rigidity of the manifold assembly by adding ribs to the outside of the manifold. Added ribbing stiffens the structure and thereby reduces vibrations in the engine system. US 2010/0326395 A1 shows an example system having ribs and braces added to the outside surface of an intake manifold cover in order to stiffen the assembly and reduce noise from vibrations within the system. An alternative approach to reducing vibrations within a system, and therefore the noise transmitted, involves adding a thin layer of absorbent material to the walls of an engine component. In US 2006/0201470 A1, a system is described wherein two walls of an engine component, e.g. an engine cover or manifold wall, is reinforced with a honeycomb layer of absorbent padding. In the three-layer system described, wherein the absorbent honeycomb layer is sandwiched between two walls, the middle layer also contains a substantial amount of air and so acts as a noise insulator to reduce vibrations and the noise transmitted.
The inventors herein have recognized the above issues, as well as limitations related to such approaches. For example, addition of structural ribs to an engine component, for instance, an intake manifold, may also increase its weight, manufacturing cost, and overall size due to the traversal of the ribs spanning various surfaces. For example, additional structural ribs may increase the manifold outside its allotted package space. Further, such additional features may slow the rate of production. For example, a plastic intake manifold made using the injection mold process may have an increased solidification time, herein referred to as the time-to-freeze. The additional thickness due to additional ribs can thus increase the time-to-freeze and slow production cycle times.
In one example approach to at least partially address these issues, an engine component with a surface, such as a plastic surface, may include a plurality of polydomal protuberances cooperating together to reduce noise and vibration. One advantage of such polydome protuberances is that the polydomes may be added in order to increase the stiffness of the engine part while limiting the increase in overall mass/size and thickness. For example, an increase in mass from addition of polydome features to a surface may be counteracted by a corresponding reduction in, for example, the thickness of the surface to which the polydomes are attached. In this way, it is possible to take advantage of the morphological features described herein to stiffen plastic materials and thereby enhance the sound qualities of the surface with respect to noise reduction. Various embodiments of polydome implementation are described with respect to size, positioning, etc. on a surface of an example engine intake manifold.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.